97 80 Series Spongy Brake Pedal (1 Viewer)

[mikeofnvfl]

Spongy brake pedal started about 3 weeks ago. No brake fluid leaks. No noise. Brakes seem to work OK. Replaced pads 3 years ago and they only have about 12K miles on them.
My next step was going to be bleed the brakes. Any suggestions?

 

[Izeloz]

If nothing else has changed other than the pedal becoming squishy (no brake bleeding before that symptom) then I would say you have a master cylinder on its way out. AFAIK, air doesn't spontaneously get into the system if it isn't opened and there are no leaks. HTH

 

[73lndcrsr]

I agree.

If nothing else has changed other than the pedal becoming squishy (no brake bleeding before that symptom) then I would say you have a master cylinder on its way out. AFAIK, air doesn't spontaneously get into the system if it isn't opened and there are no leaks. HTH

The other option, which I have not had on my 80, is the floating caliper pins sticking. On my wife's ES350, this happens yearly and I have to rebuild them. Likely something I am not doing correctly since I have to do it every year, but it is not too bad. Might be worth a check.

 

[Fox3030]

Also worth checking your wheel bearings and rotor mounting bolts as either of these can cause the pads to be pushed back and give a spongy pedal.
Often with excessive wheel bearing movement the pedal can be pumped up but quickly goes spongy again as the movement pushes the pads back.
hope this helps
cheers

 

[MickeyB]

If nothing else has changed other than the pedal becoming squishy (no brake bleeding before that symptom) then I would say you have a master cylinder on its way out. AFAIK, air doesn't spontaneously get into the system if it isn't opened and there are no leaks. HTH

Agreed, how old is the Master cylinder. Had the same issue and eventually the pedal just went to the floor. This stuff about wheel bearings and pin sticking is complete none sense.

 

[Fox3030]

Agreed, how old is the Master cylinder. Had the same issue and eventually the pedal just went to the floor. This stuff about wheel bearings and pin sticking is complete none sense.

Wow happy I joined this forum and tried to help with my previous experiences, only to get a spay in relation to my first post.
Anyway good luck finding the problem.
Cheers

 

[flintknapper]

On mine....I just tossed the sponge.

 

[Rusty Marlin]

Are you sure you don't have a leak?
My LSVP was leaking and the only way I found out about it was I bumped the rubber boot with my elbow whil working on my rear control arm bushings and it peed on me.
Might want to give the rubber boot on your LSVP a squeeze.

 

[ppc]

You may also have a failing rubber brake line hose that is bulging under pressure.

 

[MickeyB]

Wow happy I joined this forum and tried to help with my previous experiences, only to get a spay in relation to my first post.
Anyway good luck finding the problem.
Cheers

Here we go since people like to throw out random irrelevant stuff. As per my 94 FSM:

Low pedal or spongy brake pedal:
1. Brake System (Fluid leaks)
2. Brake system (Air)
3. Piston Seal (worn or damaged)
4. Rear brake (shoe clearance out of adjustment)
5. Master cylinder faulty
6. Booster push rod

There you go, nothing about wheel bearings or pins.

 

[surfpig]

Spongy brake pedal started about 3 weeks ago. No brake fluid leaks. No noise. Brakes seem to work OK. Replaced pads 3 years ago and they only have about 12K miles on them.
My next step was going to be bleed the brakes. Any suggestions?

I would definitely start by bleeding the brakes - cheap and easy. It may have never been done before. It made a world of difference on mine. The fact that it started recently probably points to some other issue that needs attention as others have mentioned.

 

[smritte]

Considering what people have posted are all real possibilities, I personally wouldn't have called them irrelevant.
The OP stated everything was fine, no leaks (which will be noticed by looking at fluid level), now has a soft pedal.
Looking at your list.
#1 brake fluid leaks. He said it wasn't loosing fluid.
#2 air. Air does not magically appear in systems and he hasn't worked on it recently. that ones out.
#3 piston seal. see #1
#4 He should have rear disk (1997)
#6 push rod. These don't go out of adjustment by themselves.

The only thing that is not listed and I would see this on high mileage vehicles is, internal leak in the ABS. This will give the same symptom as a master cyl bypassing. Inside the ABS you have a spring loaded chamber called an accumulator. It is sealed off by a "dump valve". If the dump valve seal wears, when you press on the brake, the fluid seeps past and goes into the accumulator giving a "soft pedal"

 

[MickeyB]

Considering what people have posted are all real possibilities, I personally wouldn't have called them irrelevant.
The OP stated everything was fine, no leaks (which will be noticed by looking at fluid level), now has a soft pedal.
Looking at your list.

#1 brake fluid leaks. He said it wasn't loosing fluid.
#2 air. Air does not magically appear in systems and he hasn't worked on it recently. that ones out.
#3 piston seal. see #1
#4 He should have rear disk (1997)
#6 push rod. These don't go out of adjustment by themselves.

The only thing that is not listed and I would see this on high mileage vehicles is, internal leak in the ABS. This will give the same symptom as a master cyl bypassing. Inside the ABS you have a spring loaded chamber called an accumulator. It is sealed off by a "dump valve". If the dump valve seal wears, when you press on the brake, the fluid seeps past and goes into the accumulator giving a "soft pedal"

Cool so how does one check this internal abs dump valve. Also you missed faulty master cylinder on step 5. How about we ensure all the basics are done before running down rabbit holes. So starting with number 1, he said no leaks how did they check this. We’re is vehicle located. If in Midwest or northeast could be a rust item.

 

[smritte]

If it's leaking, after the couple weeks he noticed it, the fluid level would be down. Didn't miss the master because its going to be the most common. Old lines will only cause this problem if they broke down internally and are bulging, as was mentioned.

When your dealing with a spongy pedal and an abs system, most of your service manuals have you start with a visual for leaks then a fluid flush then a master cyl replacement. Surprisingly, very few manuals will have you check caliper mounting and bearings.

There's several techniques for checking the master for bypassing. The problem now is, if the problem is still there, depending on who made the abs system, the abs check will either be easy or impossible. On the impossible systems (97 landcruiser) you just throw a new abs on it.

There's two manufactures who make an access to the back of the accumulators. You basically pop out these two rubber plugs, insert a pick in each, start vehicle and push on brake. If one of the valves is leaking, it push's the pick out.
Over the years I've seen quite a few high mileage and some low mileage (thank you ford) vehicles with this failure. If you can access the ABS computer with a scan tool, you can test the valves for sealing in some vehicles.

If you do a search in this forum, you find people battling this problem. They will flush the system a dozen ways, replace everything and still have the problem. Its when they remove the abs system, its fixed. Most people will state "you had air in the abs". Again, air does not magically appear and the problem just came about without having touched the hydraulic system.

Sadly, at the dealer level, you would be surprised how many techs don't know these basics and some don't care.

 

[smritte]

OH I forgot to add.
First rule in diagnostics. Make a mental list of ALL the possibilities.
Then, eliminate as much as you can with visual. Testing, you always start with the easiest first, eliminating things as "not the problem". Never look for what's broken, always prove what's not broken. When your done you may find the issue was a combination of failures.

People who "go down rabbit holes" normally have very little knowledge of what their doing and "guess". The OP has a pretty complete list now to start eliminating.

 

[MickeyB]

At this point who knows and who cares, OP who made the post has been silent. So that tells me it’s not a huge priority. Nonetheless I have diagnosed and fixed several things on my own having a limited knowledge just by following the FSM and doing research. These were things that the dealer and so called experts were not able to fix or did not care to because there was no money in them.

 

[Big E 27]

Also worth checking your wheel bearings and rotor mounting bolts as either of these can cause the pads to be pushed back and give a spongy pedal.
Often with excessive wheel bearing movement the pedal can be pumped up but quickly goes spongy again as the movement pushes the pads back.
hope this helps
cheers

I'm a little late on this on but I'm backing what Fox3030 said because in my case it was bearing related. The brakes could be pumped up and would remain firm if the vehicle was stationary but after driving a short distance, they would be spongy again. I jacked the front up and found the bearing pre-load on the LHS was a bit loose. This was allowing enough movement in the disc to move the pads away. I had changed the bearings a while back and cked the pre-load multiple times after putting some miles on it.
Long story short. I learned that day to put a new star tab washer on after every bearing change.
Now bag me out about lack of maintenance or poor maintenance if your are that kind of person but Fox3030s post solved my issue and probably saved my bacon.